Field of the Disclosure
The present disclosure relates to a resin-sealed module formed by resin-sealing plural circuit components mounted on a circuit substrate.
Description of the Related Art
Hitherto, the following resin-sealed module, for example, has been provided. The resin-sealed module includes a circuit substrate, plural circuit components, and a resin sealing layer. On a first main surface of the circuit substrate, plural land electrodes are formed. The plural circuit components are mounted on the land electrodes formed on the first main surface of the circuit substrate. The resin sealing layer is provided on the first main surface so as to cover the plural circuit components. The plural circuit components are mounted on the first main surface of the circuit substrate by soldering outer electrodes of the circuit components to the land electrodes.
In a resin-sealed module, outer electrodes of some of the plural circuit components may be set at the same potential. In this case, the plural outer electrodes set at the same potential may be soldered to a land electrode used for the plural outer electrodes (hereinafter referred to as a “common land electrode”) (see, for example, Patent Document 1).
FIG. 14 is a plan view illustrating a known common land electrode. As shown in FIG. 14, a known common land electrode 500 includes plural mounting sections 501 and bridge sections 502. The plural mounting sections 501 are formed in a rectangular shape and are disposed linearly. The bridge sections 502 are each disposed in an area where mounting sections 501 are opposed to each other so as to serve as a bridge for interconnecting the mounting sections 501. In the example shown in FIG. 14, two common land electrodes 500 are formed on a first main surface of a circuit substrate. The two common land electrodes 500 are arranged in parallel with each other such that each of the mounting sections 501 of one common land electrode 500 and an associated mounting section 501 of the other common land electrode 500 are disposed in parallel.
If a circuit component 503 is constituted by a chip passive element formed in a rectangular parallelepiped shape (hereinafter referred to as a “chip component”), such as an inductor, a capacitor, and a resistor, it is connected to the common land electrode 500 in the following manner, for example. An outer electrode 504 disposed at one end portion of the circuit component 503 is soldered to one of two mounting sections 501 of the common land electrodes 500 disposed in parallel. An outer electrode 504 disposed at the other end portion of the circuit component 503 is soldered to the other one of the mounting sections 501 of the common land electrodes 500 disposed in parallel. Similarly, among the three mounting sections 501 arranged in the top-bottom direction in FIG. 14, as well as to the mounting section 501 at the top position, an outer electrode 504 of a circuit component 503 is also connected to the mounting section 501 at the intermediate position and to the mounting section 501 at the bottom position, though they are not shown in FIG. 14. As a result, the three circuit components 503 are connected in parallel with each other.
Generally, circuit components 503 such as chip components are mounted on land electrodes including the common land electrode 500 on a circuit substrate in the following manner, for example. A solder paste is applied to each land electrode, and each circuit component 503 is temporarily fixed on a predetermined land electrode. Then, the circuit component 503 on the land electrode is heated in a reflow process. Due to the melting of solder in the reflow process, the outer electrodes 504 of each circuit component 503 are connected to the corresponding land electrode.
When connecting each circuit component 503 to a corresponding land electrode, the circuit component 503 is positioned on the corresponding land electrode and is temporarily fixed thereto by a component mounter. In this case, when positioning the circuit component 503 on the land electrode, misalignment may occur due to the position precision of a component mounter in positioning components. However, even with the occurrence of misalignment in the temporarily fixed circuit component 503, the following so-called self-alignment phenomenon is produced. Surface tension generated when solder on the land electrode melts in the reflow process is applied to the circuit component 503, so that the circuit component 503 moves toward the land electrode on which a large amount of molten solder is positioned, thereby offsetting the misalignment. Accordingly, even upon the occurrence of misalignment when temporarily fixing the circuit component 503 on the land electrode, the circuit component 503 moves back to the design position due to the self-alignment phenomenon, which is produced when a solder paste applied to the land electrode melts in the reflow process, thereby offsetting the misalignment.
However, in a case in which the outer electrodes 504 of the plural circuit components 503 are soldered to the common land electrode 500, such as that shown in FIG. 14, the following problem may occur. The common land electrode 500 includes the plural mounting sections 501. Depending on a direction of the misalignment of a circuit component 503 to be temporarily fixed on the common land electrode 500, the surface tension of molten solder on the mounting section 501 adjacent to that on which the circuit component 503 should normally be disposed (hereinafter such a mounting section will be referred to as a “target mounting section”) may act more strongly on the circuit component 503 than that on the target mounting section. Thus, the temporarily fixed circuit component 503 with some misalignment may move toward the mounting section 501 adjacent to the target mounting section 501, which may increase the misalignment to an even greater amount.
If there is a misalignment in a circuit component 503 toward an adjacent mounting section 501 after the reflow process, the gap (distance) between the misaligned circuit component 503 and the circuit component 503 disposed on the adjacent mounting section 501 is reduced. If the gap between the circuit components 503 is reduced, resin-charging properties in charging resin between the circuit components 503 are decreased. Accordingly, when forming a resin sealing layer used for resin-sealing circuit components mounted on a first main surface of the circuit substrate, the resin may not fill properly a small gap between circuit components 503, which may produce hollows in the resin sealing layer.
As a result, when a resin-sealed module with hollows in a resin sealing layer is mounted on an outer substrate, such as a mother substrate, the following problem may occur. Due to the heat in the reflow process, the air or moisture within the hollows formed in the resin sealing layer rapidly expands, that is, the so-called popcorn phenomenon may occur. Additionally, the reliability of the resin-sealed module may also be decreased.
Hence, in order to prevent the occurrence of the misalignment of the plural circuit components 503 to be connected to the common land electrode 500, the common land shown in FIG. 14 is formed in the following manner. The line width of the bridge sections 502 positioned on a straight line (imaginary line) L indicated by the long dashed dotted line in FIG. 14 is formed smaller than the width of the mounting sections 501. The straight line L connects the centers of the edges of mounting sections 501 in the area where the mounting sections 501 are opposed to each other. The direction in which the distance between opposing mounting sections 501 is minimized is indicated by the straight line L.
It is now assumed that a circuit component 503 to be connected to a predetermined mounting section 501 of the common land electrode 500 is temporarily fixed in a state in which it is misaligned toward an adjacent mounting section 501. In this state, when molten solder on the mounting section 501 melts, the following misalignment may occur in the circuit component 503. Due to the generation of the surface tension of molten solder on the adjacent mounting section 501, the circuit component 503 moves toward this adjacent mounting section 501 by taking the shortest route. Accordingly, the circuit component 503 may move toward the adjacent mounting section 501 by passing on the straight line L where the distance between the adjacent mounting sections 501 is minimized.
However, since the line width of the bridge sections 502 positioned on the straight line L is formed smaller than the width of the mounting sections 501, as shown in FIG. 14, the amount of molten solder on the bridge sections 502 is smaller than that on the mounting sections 501. Accordingly, if the circuit component 503 is misaligned toward the adjacent mounting section 501 and is temporarily fixed on the bridge section 502 such that it partially overlaps the bridge section 502, the surface tension of molten solder acts on the misaligned circuit component 503 in the following manner. As the amount of molten solder is greater, surface tension becomes stronger. Thus, the surface tension generated by the molten solder acting in the direction toward the target mounting section 501 becomes stronger than that toward the adjacent mounting section 501 (bridge section 502). As a result, due to the occurrence of the self-alignment phenomenon, the circuit component 503 is disposed on the target mounting section 501.                Patent Document 1: Japanese Unexamined Patent Application Publication No. 4-317386 (paragraph 0012, FIG. 1, etc.)        